Propellants containing nitrocellulose



United States Patent 3,364,086 PROPELLANTS CONTAINING NITROCELLULOSE Wilhelm Oversohl, Manuel Segura, and Stanislaus Blotz, Waldkraihnrg, Germany, assignors to Nitrochemie, G.m.b.H. Mulildorf, Upper Bavaria, Germany, a corporation of Germany N0 Drawing. Filed Dec. 9, 1965, Ser. No. 512,813 Claims priority, application Germany, Dec. 9, 1964, N 25,948 10 Claims. (Cl. 149-2) ABSTRACT OF THE DISCLOSURE A novel method of producing solid propellants having a high rate of combustion and to the products produced by said method. More particularly, this invention relates to a method of preparing solid propellants from nitrocellulose granules and to the highly combustible product produced thereby.

Prior art For specific purposes, for example, for booster charges, post acceleration charges and short period burners, it is desirable to use solid propellants which possess the highest possible rate of combustion.

In the past, and with certain types of charges, it has been the practice to increase the rate of combustion by increasing the fineness of the grain size of the charge component used, and in specific instances by integral casting of metal wires in the charge. Thus, in cast compositions based, for example, on amnionitimperchlorateorganic bonds, the rate of combustion has been increased by regulating the fineness of the grain size of the ammonium perchlorate. Also, in certain instances, for example, front burners, the integral casting of metal wires has been found to increase the combustion rate.

In View of the importance of solid propellants other methods have been sought for increasing their rates of combustion. Of interest are the solid propellants containing nitrocellulose, and of particular interest are the socalled POL compositions, i.e. powder without solvent.

Objects of the invention Accordingly, it is an object of this invention to provide a method for increasing the rate of combustion of solid propellants.

Another object of this invention is to provide a method for increasing the rate of combustion of solid propellants containing nitrocellulose.

A further object of this invention is to provide a method for increasing the rate of combustion of POL solid propellants containing nitrocellulose.

Another object of this invention is to provide a method for increasing the rate of combustion of cast POL solid propellants containing nitrocellulose.

Another object of this invention is to provide solid propellants having a high rate of combustion.

Another object of this invention is to provide solid nitrocellulose propellants having a high rate of combustion.

Still another object of this invention is to provide POL solid nitrocellulose propellants having a high rate of combustion.

Another object of this invention is to provide cast POL solid nitrocellulose propellants having a high rate of combustion.

A further object of this invention is to provide a method for producing porous nitrocellulose granules.

3,364,086 Patented Jan. 16, 1968 ice The invention Accordingly, it has been discovered that it is possible to obtain fast burning charge compositions by using porous nitrocellulose as a charging granules in cast POL propellants, i.e. powder without solvent propellants. The porosity of the nitrocellulose granules may be effected during the preparation thereof by working in Water soluble salts and by subsequent extraction of these salts.

The cast POL propellants are prepared, for example, by admixing the nitrocellulose granules with polyalcohol nitrates, such as nitroglycerin and other liquid plasticizers, to a mass capable of being cast, which mass is then poured into a mold of the proper shape. By subsequent heat treatment, the nitrocellulose granules gelatinize and the entire mixture sets up into a homogeneous mass.

The nitrocellulose granules are prepared from nitrocellulose or nitrocellulose compositions which are capable of gelatinization in the nitroglycerin and other plasticizers used in making the cast composition. The compositions used in preparing the nitrocellulose granules may contain stabilizers, solvents and other ingredients. The composition is thereafter gelatinized in a kneading apparatus under the addition of a water soluble salt. The gelatinized mixture is then extruded, the strands obtained cut into appropriate size, and the solvents and salts removed. The granules are thereafter compounded with the appropriate ingredients for preparation of the cast charge.

In order that the porosity of the nitrocellulose granules be retained during the preparation of the cast charges, the nitrocellulose should be of a type that does not gelatinize all the way through under the conditions employed for the preparation of the cast charges. In other words, the nitrocellulose should be capable of partial gelatinization. In order to accomplish this, it was found that a nitrocellulose having a nitrogen content of about 12.9 to 13.2% produces the desired degree of gelatinization under the condition employed for preparing the cast charges. The nitrogen content may, however, fall below or may exceed this percentage according to the heat treatment employed in casting the charges.

The rate of combustion of the charges of this invention may be controlled to a large extent by the gradation of the porosity of the nitrocellulose granules used. The porosity, in turn, may be controlled by the amount and grain size of the water soluble salt utilized in producing the porous nitrocellulose granules. The greater the amount of water soluble salt used, the greater the porosity, and thus the faster is the rate of combustion. Any Water soluble salt may be utilized for the preparation of the granules. Salts such as alkali metal sulfates, chlorides and nitrates may be used. Good results have been produced using potassium nitrate, sodium nitrate or sodium chloride. When, for example, sodium chloride is used, its content may be varied fromabout 10 to 300%, by weight based on the content of nitrocellulose. By decreasing the grain size of the salt, the porosity of the nitrocellulose granules increases, thereby increasing the rate of combustion of the finished charge. As a rule, the average grain size of the Water soluble salt should be about 50 t0 ZOO/1..

By using a nitrocellulose with a higher nitrogen content a further acceleration of the combustion rate is also possible. Thus, rates of combustion of about 20 mm./ sec. to mm./sec., at a pressure of 70 atmospheres and at a temperature of 20 C. may be obtained.

It is possible to mix porous nitrocellulose granules with non-porous granules and thereby vary the rate of combustion and ballistic characteristics of each cast 3 batch. Thus, for example, about to 90%, by weight, of porous granules may be combined with 90 to 10%, by weight, of non-porous granules.

The rate of combustion may be further accelerated by any of the conventional methods heretofore known. For example, metal wires may be worked into the cast charges.

The charge compositions to which this invention is applicable are any of the presently known nitrocellulose solid propellant systems. Depending upon whether the compositions contain only nitrocellulose, have nitroglycerin as a second combustible ingredient, or contain nitroguanidine in addition to nitroglycerin and nitrocellulose, these propellants are known as single-, double-, or triple-base. The following table lists the general types of material, the range of percentages for typical nitrocellulose propellants, together with some examples of typical ingredients.

TABLE I Range of '1 ypc l\1atcria1 Content Example (Percent) Basic ingredient 40-90 Nitrocellulose. Stabilizer l-2 Diphcnylamine.

llasticizer:

(a) N on-explosive (b) Explosive 0-30 Dieth ylphth alate.

0-50 Nitroglyeerin. Darkening agents. 0-. 2 Carbon black. Ballistic agents". 0-3 Potassium sulfate. Other additives A. 0-2 Candclilln. wax. Solvents (processing) 0-40 Alcohol-ether, acetone.

To the castable mixtures of the invention, according to the end characteristics desired for the charge, other inorganic oxidizing agents may be added. For example, perchlorates or nitrates such as potassium perchlorate, ammonium perchlorate, or ammonium nitrate may be added. The inorganic oxidizing agent may be used expediently in amounts of about 20 to 40%, by weight, of the total composition.

The following examples illustrate the invention, but are not to be construed as in anyway limitative thereof.

EXAMPLE I 75.0 kg. nitrocellulose (13.1% N) moistened with an aqueous ethanol mixture containing 28% ethanol 82.0 kg. of sodium chloride 0.525 kg. of dibutylphthalate 1.24 kg. of diphenylamine 0.04 kg. of graphite The above composition was gelatinized in a mixture of 6 liters of ethanol and 90 liters of ether. This batch, after gelatinization, was then pressed through a matrix having a 1.8 mm. diameter and then cut into lengths of 1.8 mm. to form individual granules. The granules were then soaked in water for about 40 hours at a temperature of 40 to 65 C. to remove the solvent and the sodium chloride. Thereafter, the granules were air dried to produce the porous granule.

EXAMPLE II In a mixer commonly used for the preparation of explosives, 45.5 kg. of the porous granules as prepared in Example I were mixed with 41.0 kg. of nitroglycerin and 13.5 kg. of triacetin for about minutes. The viscous batch was then filled into the charge mold and shaken for about 10 minutes. After being held in a warming cabinet for 3 days at a temperature of 50 to 55 C., the charge was hardened.

The rate of combustion of the cast charge thus prepared was measured in the Crawford Bomb and found to be mm./sec. at a pressure of 10 atmospheres and 20 C.

EXAMPLE III This example demonstrates a charge containing porous and nonporous nitrocellulose. Non-porous nitrocellulose granules were prepared with the following components:

In preparing the above composition, the alcohol moist nitrocellulose was admixed in a kneading apparatus of 400 liter capacity with centralite I, acardite 11, lead salicylate and polyacetylene for 20 minutes. Next, the lead ethylhexoate, diluted with 5 liters of warm alcohol, was added to this mixture, and the batch was kneaded for 20 minutes more. Thereafter, a mixture of ether and alcohol, in equal parts, were added and then the mass was kneaded for 3 hours more. For each parts of nitrocellulose parts of solvent were used.

The kneaded batch Was stored for 1 day in sealed containers for the purpose of aging. Thereafter, the mass was pressed into strands over an unheated press through matrices of 1.5 mm. to 2 mm. in diameter. These strands were then cut to a length of 1.5 to 2 mm. in the cutter to form granules. The granules, in a solvent-moist condition, were subsequently dried for 3 to 5 days at a temperature of 50 to 60 C., and then freed of under-and over-size granules by screening.

The batch used for pressing was homogeneous, well gelatinized and of gummy consistency. For pressing out the strands a pressure of 160 to 200 kg./cm. was required.

Into a mixer, the non-porous cellulose granulate prepared as previously described, plasticizers, nitroglycerin and the porous nitrocellulose granules prepared according to Example I, were charged and kneaded for about 20 hours at normal temperature. This mixture was filled into casting molds and treated for about 10 minutes on a jarring table. The hardening of the batch took place at 50 C. over a period of 3 days.

The composition of this type of batch was as follows:

Weight percent Solid granules 26.00 Porous granules 22.5 Plasticizers 8.0 Nitroglycerin 43.5

The ballistic additives and the stabilizers were worked in during the preparation of the granules.

The batch had an explosion heat of 940 kcaL/kg. The rate of combustion in the Crawford Bomb amounted to 75 mm./sec. at a pressure of 70 atmospheres and a temperature of 20 C.

EXAMPLE IV A cast charge was prepared according to Example III, except that all of the porous granules were substituted by non-porous granules.

The rate of combustion was only 20 mm./sec. at a pressure of 70 atmospheres and a temperature of 20 Ct as measured in the Crawford Bomb.

While certain specific examples and preferred modes of practice of the invention have been set forth it will be understood that this is solely for the purposes of illustration and that various changes and modifications may be made without departing from the spirit of the disclosure and the scope of the appended claims.

We claim:

1. A process for the preparation of cast solid nitrocellulose propellants which comprises:

gelatinizing nitrocellulose in the presence of a watersoluble salt;

forming granules from the gelatinized nitrocellulosesal-t mixture;

removing the water-soluble salt from the thus formed granules to produce a porous granule;

suspending said porous granule in a propellant comprised of nitroglycerin;

filling the propellant composition into a casting mold and heating the cast propellant in the mold to effect gelatinization and to obtain a homogenous body.

2. A process according to claim 1, wherein said watersoluble salt is used in an amount of from to 300%, by weight, based on the content of nitrocllulose.

3. A process according to claim 1, wherein said watersoluble salt has a grain size of about 50 to ZOO/1..

4. A process according to claim 1, wherein said nitrocellulose has a nitrogen content of from about 12.9 to 13.2%.

5. The process of claim 1 wherein the cast propellant contains metal Wires.

6. The process of claim 1 wherein the porous nitrocellulose contains at least one member selected from the group consisting of stabilizers, plasticizers, agents and ballistic additives.

7. The process of claim 1 wherein up to 90% of the nitrocellulose in the cast propellant is non-porous nitrocellulose granules.

8. The process of claim 1 wherein the cast propellant contains 20 to by weight of the total composition of an inorganic oxidizing agent.

9. A cast solid rocket propellant produced by the process of claim 1.

10. A process for the preparation of cast solid nitrocellulose propellants which comprises:

gelatinizing nitrocellulose having a nitrogen content of about 12.9 to 13.2% in the presence of from 10 to 300%, by weight, based on nitrocellulose, of a watersoluble salt having a grain size of about to 200p;

forming granules from the gelatinized nitrocellulose salt mixture;

removing the water-soluble salt from the thus formed granules to produce a porous granule;

suspending said porous granule in a propellant comprised of nitroglycerin;

filling the propellant composition into a casting mold and heating the cast propellant in the mold to effect gelatinization and to obtain a homogenous body.

References Cited UNITED STATES PATENTS CARL D. QUAR FORTH, Primary Examiner. LELAND A. SEBASTIAN, Examiner. 

